Antagonistic Competitive Equilibrium Modeling for the Adsorption of Ternary Metal Ion Mixtures from Aqueous Solution onto Bagasse Fly Ash

The present study reports the simultaneous adsorption of cadmium (Cd(II)), nickel (Ni(II)), and zinc (Zn(II)) ions from aqueous solution onto bagasse fly ash (BFA). BFA is a waste material collected from the particulate collection equipment attached to the flue-gas line of bagasse fired boilers in sugar mills. The equilibrium adsorption data were obtained with a BFA dosage of 10 g/dm3 at varying initial concentrations (C0 = 10−100 mg/dm3), 5 h contact time, 30 °C temperature, and initial pH 6. The single metal ion equilibrium adsorption data were fitted to the noncompetitive Langmuir, Freundlich and Redlich−Peterson (R−P) models. The R−P and Freundlich models represent the equilibrium data better than the Langmuir model over 10 ≤ C0 ≤ 100 mg/dm3. The adsorption capacity of Zn(II) is found to be higher than that of Ni(II) or Cd(II) for the ternary metal solutions, and is in agreement with the single-component adsorption data. The equilibrium metal removal decreases with an increase in the concentration of the other metal ion and the combined action of Cd(II), Ni(II), and Zn(II) ions on BFA is generally found to be antagonistic. Equilibrium isotherms for the ternary adsorption of Cd(II), Ni(II), and Zn(II) ions on BFA have been analyzed by using nonmodified, modified, and extended Langmuir models; nonmodified and modified R−P models; and the Sheindorf−Rebuhn−Sheintuch (SRS) model. The competitive SRS model fits the ternary adsorption equilibrium data satisfactorily and adequately, and has been used to simulate the equilibrium sorption behavior of the ternary metal ion system through three-dimensional plots.